Organic electroluminescent devices, also called organic electroluminescent diode (OLED) devices, belong to a brand new display technique. OLED is comparable to that of thin film transistor liquid crystal display (TFT-LCD) in terms of display quality, but its price is much lower. OLED has become a hot spot of international research for its significant advantages in panel display such as high luminescence, colorful display, low-voltage DC drive and simple manufacture process. Within less than 20 years, OLED has entered industry stage from research stage.
Generally, OLED devices are formed by depositing a transparent anode layer, a metal cathode layer and more than two organic luminescent layers sandwiched therebetween onto a supporter such as a rigid glass substrate or a flexible polymer substrate. These organic luminescent layers generally comprise hole injection layers, hole transporting layers, luminescent layers, electron transporting layers, electron injection layers and the like. OLED devices are very sensitive to oxygen and vapor. If oxygen and vapor leak into the OLED devices, undesirable phenomena such as black spots, pinholes, electrode oxidation and chemical reactions of the organic materials would occur, which would affect the lifetime of OLED devices. Therefore, encapsulation technology is one of the major technologies that have realized the industrialization of OLED devices.
At present, encapsulation technologies mainly comprise three categories: metal cover encapsulation, glass cover encapsulation and film encapsulation. In the former two categories, sealants have to be disposed around the organic luminescent area, and moisture absorbents have to be placed therein. Multi-layered structures with alternate organic polymer films and inorganic films, which are manufactured on the basis of a vacuum coating process, have been adopted in film encapsulation technology. In this multi-layered structure, the inorganic film functions as a main water and oxygen barrier layer for its high compactness; and the organic polymer film functions as a buffer layer because it can effectively inhibit cracking of the inorganic films for its high elasticity.